1. Field of the Invention
The present invention relates generally to reinforced catheter probe structures and more particularly pertains to the enhancement of the tensile strength of optical fiber containing sensor devices that are intended for intravascular introduction so as to effectively minimize or preclude the risk of detachment of a distal portion thereof.
2. Description of the Prior Art
A variety of sensor systems have been developed that require the introduction of an optical fiber or optical fiber bundle into a patient's vasculature in order to obtain real time measurement of certain physiological parameters. In order to expand the capabilities of such systems, sensor probes are being called upon to accommodate an increasing number of components therein while maintaining a very small outside diameter. These requirements constrain the individual components to be of reduced size and consequently, optical fibers of very small cross-section are used. Such optical fibers are relatively delicate and have little individual strength. Furthermore, when the optical fibers are displaced about the central axis of the sensor probe, they are subjected to increased stress in bending and are thus more susceptible to fracture. Invasive optical blood gas analyzers have been proposed that employ a sensor probe incorporating a plurality of optical fibers for sensing a number of parameters, including the partial pressure of oxygen, the partial pressure of carbon dioxide, pH and blood temperature. Such sensors are particularly susceptible to fracture of the fibers due to bending or rough use.
Mechanical failure of such a sensor probe while it is inserted within a patient's vasculature could result in a portion of the sensor probe being carried into the blood stream with the resultant undesirable consequences, especially if the severed section of the sensor probe were carried to a critical area within the vasculature. It is therefore desirable to provide sensor probes with an internal member having sufficient tensile strength to avoid the likelihood of severance of a portion of the sensor probe tip if the fibers in the sensor probe are broken.
An additional important consideration in the design of such sensor probes is cost. Such sensor probes are intended for a one-time use only and risks of infection and the degradation of the sensors performance upon resterilization preclude the re-use of such devices. The sensor probes, including any provisions for enhancing tensile strength, must therefore be manufacturable as inexpensively as possible in order to render their disposability economically feasible.
The mechanical strength and more particularly, the tensile strength of some prior art optical fiber-containing sensor probe systems has been increased by the incorporation of a stainless steel wire disposed within the sensor probe and parallel to the optical fibers. The distal end of the wire is welded to a stainless steel spherical anchor element, the outer diameter of which conforms to or slightly exceeds the outer diameter of a sheath that envelops the optical fiber bundle. A portion of the sheath may similarly be constructed of stainless steel and welded to the anchor element. While such a configuration presumably imparts substantial tensile strength to the sensor probe system and prevents detachment of the tip if the optical fibers are broken, this configuration is incompatible with systems that require the distal end of the sensor probe to be fully exposed to blood flow. Further, the stainless steel components and the rather labor-intensive effort required for its assembly add substantial cost to the sensor probe.
It has also been found that optical fiber based sensor probes have a tendency to break where the strain of bending is imposed on the sensor probe. Such sensor probes are typically disposed within a conventional introducer catheter having a relatively inflexible hub or funnel portion and a relatively flexible elongated tubular portion. Breakage of the sensor typically occurs at the junction of the hub and flexible tubular portion within the introducer catheter due to the force of bending which can be imposed on the optical fiber portion of the sensor probe there.
It would be highly advantageous if a low cost means were available which substantially enhanced the tensile strength of an optical fiber sensor probe system, particularly if one or more optical fibers is fractured, allowed free access of an analyte to the distal end of the sensor probe and which protected and did not impair the flexibility of the sensor probe. The present invention provides such a capability.